1. Field of the Invention
The present invention relates in general to electrochemical cells, and more particularly, to secondary electrochemical cells having a passivating additive that substantially precludes the formation of gas within the electrochemical cell as a result of decomposition of solvents contained within the electrolyte, and wherein the additive itself does not form a gas from its own decomposition during cell cycling and storage. The present invention also relates to a secondary electrochemical cells excellent in rate characteristics and a capacity retention percentage after repeating charge and discharge cycles.
2. Background Art
Lithium ion batteries have been known in the art for several years. Furthermore, lithium ion batteries comprising carbonaceous electrodes and liquid, gel, polymer, or plastic electrolytes are likewise well known. While these electrolytes have been readily utilized, problems have been identified with respect to commercial solvents, contained within the electrolytes, decomposing during cell cycling and storage. In particular, without the presence of at least a conventional additive within the cell to form a passivating layer, the solvent reacts with the carbonaceous surface of the electrode and partially decomposes during an initial charge. This decomposition, in turn, results in the formation of gas which adversely affects the cell""s electrochemical performance.
Although conventional additives have been used to form a passivating layer which substantially prevents the solvent from contact and subsequent decomposition with the carbonaceous electrode, problems nevertheless persist. Specifically, the additive itself undergoes decomposition during cell cycling and storage, which results in the generation of significant amounts of gas within the cell.
Further, by using the conventional additives, there is a problem that essential properties of electrochemical cell such as rate characteristics and a capacity retention percentage after repeating charge and discharge cycles are deteriorated.
An object of the present invention is to provide an electrochemical cell having an additive that, among other things, remedies the aforementioned detriments and/or complications associated with the use of a conventional additive.
As a result of the present inventors"" earnest study, it has been found that by using additives having specific chemical structure, the above problem can be solved.
In the first aspect of the present invention, there is provided an electrochemical cell having a controlled electrode surface, comprising:
a first electrode and a second electrode wherein at least one of the first and second electrodes has a carbonaceous surface;
an electrolyte containing at least one solvent;
an additive associated with the carbonaceous surface of at least one of the first and second electrodes, wherein the additive comprises a compound having a molecular weight of not less than 105 and represented by the formula: 
wherein A is a group represented by: 
wherein X is a group represented by the formula: 
or linear or branched alkyl group containing 1 to 12 carbons,
wherein n is 0, 1, 2, or 3; and
wherein Ra, Rb, Rc, R1, R2, R3 and R4 are independently hydrogen or a linear or branched alkyl group containing 1 to 12 carbons.
In the second aspect of the present invention, there is provided an electrochemical cell having a controlled electrode surface, comprising:
a first electrode and a second electrode wherein at least one of the first and second electrodes has a carbonaceous surface;
an electrolyte containing at least one solvent;
an additive associated with the carbonaceous surface of at least one of the first and second electrodes, wherein the additive comprises a compound having a molecular weight of not less than 105 and represented by the formula: 
wherein A is a group represented by: 
wherein X is a group represented by the formula: 
or a linear or branched alkyl group containing 1 to 12 carbons,
wherein n is 0, 1, 2, or 3; and
wherein B is a group represented by: 
wherein R1, R2, Ra, Rb, Rc, R11, R12, R13, R14, R15, R16, R17 and R18 are independently hydrogen or a linear or branched alkyl group containing 1 to 12 carbons.
In the third aspect of the present invention, there is provided an electrochemical cell having a controlled electrode surface, comprising:
a first electrode and a second electrode wherein at least one of the first and second electrodes has a carbonaceous surface;
an electrolyte containing at least one solvent;
an additive associated with the carbonaceous surface of at least one of the first and second electrodes, wherein the additive comprises a compound having a molecular weight of not less than 105 and represented by the formula: 
wherein A is a group represented by: 
wherein X is a group represented by the formula: 
or a linear or branched alkyl group containing 1 to 12 carbons,
wherein n is 0, 1, 2, or 3;
wherein B1 and B2 are independently hydrogen, a linear or branched alkyl group containing 1 to 12 carbons or a group represented by: 
wherein R, R1, R2, Ra, Rb, and Rc are independently hydrogen or a linear or branched alkyl group containing 1 to 12 carbons.
In a preferred embodiment of the invention, the above-identified electrochemical cells further comprise means associated with the additive for substantially precluding gas formation within the electrochemical cell as a result of decomposition of the additive during cell cycling and storage.
In another preferred embodiment of the invention, the above-identified electrochemical cells further comprise means for increasing first cycle coulombic efficiency of the electrochemical cell relative to an electrochemical cell without the additive. In this embodiment the efficiency increasing means comprises the additive.
In yet another preferred embodiment of the invention, the additive is substantially soluble in the solvent of the electrolyte at ambient temperature.
In an alternative embodiment of the invention, the additive is substantially insoluble in the solvent of the electrolyte at ambient temperature.